The objectives of this project are to determine how 2450 MHz microwave radiation interacts with biological material at the cellular and sub-cellular level, to observe any effects of this interaction, and to relate the amount of microwave energy absorbed to the effect. The biological specimens have included mitochondria, cardiac cells, lysosomes, and cellular enzymes. For these experiments, a waveguide apparatus has been used which can maintain the specimens at 30 C at specific absorption rates up to 100 mW/g. For tightly or loosely coupled mitochondria using succinate as substrate, no effect of exposure was observed on respiration states 1-4 or the respiratory control index. When glutamate was used as substrate, no effects were observed at 10 mW/g. However, in the loosely coupled mitochondria, the 100 mW/g exposure produced an increase in respiration states 2 and 4 and a decrease in the respiratory control index. The results suggest the function of loosely coupled mitochondria can be affected at high power levels of microwave radiation.